Femtosecond infrared pump–stimulated Raman probe spectroscopy: the first application of the method to studies of vibrational relaxation pathways in the liquid HDO/D2O system

Abstract

We have proposed and constructed a setup for a novel method of ultrafast vibrational spectroscopy: femtosecond infrared pump–stimulated Raman probe spectroscopy. This is the first time-resolved spectroscopy providing simultaneously a sub-100 fs time resolution, a spectral resolution better than 10 cm⁻¹ and a spectral window covering an extremely broad range of molecular vibrations (at least: 200–4000 cm⁻¹) with a “single laser shot”. The new method was applied to study vibrational relaxation pathways in the liquid HDO/D₂O system. We determined the lifetimes of OH stretching vibrations to be in the range 310–500 fs depending on the isotopic dilution, which is in good agreement with the results from pump–probe femtosecond infrared spectroscopy. Moreover, we observed a strong coupling of OH stretch to OD stretch vibrations and possibly also to the librational modes of water.